Sputter coating is commonly employed in the formation of films on substrates in the manufacture of semiconductor devices, and planar magnetrons have long been used as sputtering devices to coat silicon wafers with various materials, such as aluminum, during the manufacture of integrated circuits.
With sputter coating, it is difficult to form a uniform thin film, or step coating, which conforms to the shape of a workpiece where a step occurs, e.g. at the upper or lower corner of an opening such as a hole or a via in the surface of a workpiece. It is also difficult to fill small openings (e.g. one micron, or less, in diameter or width) and to provide controlled film growth on the side and bottom walls of such openings. These difficulties arise because particles tend to leave the source in all directions, then collide with each other and scatter, arriving at the workpiece from a variety of angles. Particles which arrive at angles greater than about 45 degrees from normal to the workpiece surface tend to produce lateral growth on the surface, rather than impinging upon the walls of the openings. This lateral growth can result in overgrowth at the tops of the openings which can eventually close off the openings and prevent the particles from entering the openings.